While colonoscopy is proven to decrease colorectal cancer (CRC) fatalities, its expense, complications and limited availability makes it impractical for general population screening. Risk-stratification through assessment of the "field effect" of colon carcinogenesis can be used to determine the need for colonoscopy;however current markers (e.g. distal colonic adenomatous polyp) are clearly inadequate. Dr. Backman's group and colleagues, having pioneered light-scattering technologies for detecting dysplastic cells (Nature 2000 &Nature Med 2001), now have developed four-dimensional light-scattering fingerprinting (4D-ELF), which enables quantitative analysis of nano-scale cellular architecture. Using 4D-ELF, we discovered spectral markers in histologically normal mucosa that preceded all conventional biomarkers of experimental CRC (Gastroenterology 2004). Evaluating 4D-ELF signatures from the uninvolved rectal mucosa had unprecedented sensitivity and positive predictive value (>98%) for the future occurrence of neoplasia. Pilot human studies confirmed the promise of these novel biomarkers. We propose to further validate these spectral markers by using an endoscopically-compatible 4D-ELF probe during colonoscopy. Based on rectal 4D-ELF analysis from 500 patients, we will formulate prediction rules for both the occurrence of advanced polyps/cancers and the exclusion of neoplasia (thus identifying a subgroup not requiring further screening). We will prospectively test these rules in 750 patients. Furthermore, we will use hereditary nonpolyposis colorectal cancer and familial adenomatous polyposis as a paradigm to investigate whether the unparalleled sensitivity of 4D-ELF may detect long-term CRC risks engendered by an inherited predisposition. We will evaluate the ability of spectral marker to both identify mutations and forecast phenotypic presentation. In the future these spectral markers may be assayed with a 4D-ELF probe during rectal examination, thus providing a practical and accurate means of determining the optimal CRC screening regimen.